The present invention relates to a throttle apparatus for an engine for electrically performing control for a throttle valve angular position by means of a throttle actuator.
In the recent years, according to advancing of an electronic control for an engine, there has been proposed a technology for controlling an angular position of a throttle valve by detecting a position of an accelerator pedal (accelerator operating rate) by means of an accelerator position sensor and driving a throttle actuator (DC motor, stepping motor and so forth) on the basis of an accelerator position sensor signal and a control signal, such as, a traction control signal and so forth.
Recently, in a system for electrically controlling the angular position of the throttle valve as set forth above, there have been proposed technologies, in which an angular position of the throttle valve at OFF position of an engine key (in other words, while an electric power is not supplied to a throttle actuating motor: initial throttle valve angular position) is set at an angle greater than a minimum angle of the throttle angular position (normally, an idling opening of the throttle valve in a steady state of the engine after warming up) in a control range of the throttle valve angular position, within which the throttle valve angular position is controlled by means of the throttle actuating motor (see PCT National Publication No. 2-500677(1990), Japanese Patent Application Laid-Open No. 3-271528(1991), Japanese Patent Application Laid-Open No. 4-203219(1992), for example).
One reason why the initial opening is set at the foregoing position, is to satisfy a demand for preventing sticking of the throttle valve due to deposition of a viscosity matter, ice or the like. In addition, the initial opening set forth above is intended to assure self-travel (limp home) even upon failure of a throttle control system, and to certainly provide sufficient air flow rate for preventing the engine from stalling.
An initial opening setting mechanism (occasionally referred to as default mechanism) sets a position (close to a fully closed position of the throttle valve) where a spring force of a return spring biasing the throttle valve in a closing direction and a spring force of an initial opening spring for biasing the throttle valve in an opening direction, are balanced, as the initial opening, in principle.
In the throttle apparatus having the initial opening setting mechanism of the type set forth above, when an engine key is turned-on, for example, the throttle valve is mechanically driven from the foregoing initial opening to the minimum point of motor control (position contacting with an adjusting screw) by means of the throttle actuating motor. Thereafter, an angular position of the throttle valve is controlled at a position corresponding to an engine coolant temperature and so forth.
In an engine control portion, sensors, such as an air flow sensor, a throttle position sensor and so forth, have to be provided in an air intake system. When mechanical parts, such as the throttle actuator, gear and so forth are mounted in addition to the foregoing sensors, number of parts can be increased. On the other hand, a space in the engine room is limited.
In an electronically controlled throttle apparatus (hereinafter occasionally referred to as "electronic throttle apparatus"), a technology for aggregating and rationalization of initial opening setting mechanism, such as sensor parts, actuator parts and so forth has been held immature. Therefore, optimal installation technology has been strongly demanded. Particularly, it is typical to provide a body of the air flow sensor and the throttle body, separately. When such prior art is applied to the electronic throttle apparatus, electronic control parts and mechanical parts, such as sensor parts, actuators and so forth, are straggled to increase work load in assembling operation and wiring operation in the case where the throttle apparatus is installed in the engine room. Also, it is not easy to avoid interference between the throttle apparatus and other parts due to limitation of the space in the engine room.